• Progress in Medical Physics
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• v.6 no.2
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• pp.41-50
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• 1995

The absorbed dose and contaminant electron distribution of therapeutic X-ray beam (15MV photon) was studied with a half blocked beams of 30$\times$30$\textrm{cm}^2$ and field size ranging from 5$\times$5 to 30$\times$30$\textrm{cm}^2$. For a 15MV photon beam energy, the value of the depth of dose maximum, d$_{max}$, gradually decrease with increasing field size from 5$\times$5 to 30$\times$30$\textrm{cm}^2$ due to mainly by contaminant electrons which are produced in the flattening filter and scattered by collimator jaws, tray holder〔Lucite〕, blocking block and air. The results suggest that separate dosimetry data should be kept for blocked and unblocked field. The inherence of the contaminant electrons to the open field depth of maximum dose can lead to mistaken results if attenuation measurements are made at that depth. A nurmerous contaminant electrons mainly were distributed as shape of corn in the central photon beam and their path length in the water were shorter than 30mm because of the electrons energy having around 6MeV. These results clearly appears that the substraction of scattered electrons (electrons and positrons) from the total depth dose curve not only lowers the absolute dose in the bulidup region and surface dose, it also causes a shift of d$_{max}$ to a deeper depth. In the terapeutic high energy photon beam, the absorbed dose near the buildup region is the combined result of incident contaminant electrons and phantom generated electronsrons.

• Journal of Radiation Protection and Research
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• v.24 no.4
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• pp.195-203
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• 1999

It is difficult to determine dosimetric characteristics for small field photon beams since such small fields do not achieve complete lateral electronic equilibrium and have steep dose gradients. Dosimetric characteristics of small field 4, 6, and 10 MeV photon beams have been measured in water with a diamond detector and compared to measurements using small volume cylindrical and plane parallel ionization chambers. Percent depth dose (PDD) and beam profiles for 6 and 10 MeV photon beams were measured with diamond detector and cylindrical ion chamber for small fields ranging from $1{\times}1\;to\;4{\times}4cm^2$. Total scatter factors($S_{c,p}$) for 4, 6, and 10 MeV photon beams were measured with diamond detector, cylindrical and plane parallel ion chambers for small fields ranging from $1{\times}1\;to\;4{\times}4cm^2$. The $S_{c,p}$ factors obtained with three detectors for 4, 6, and 10 MeV photon beams agreed well ($\pm1.2%$) for field sizes greater than $2{\times}2,\;2.5{\times}2.5,\;and\;3{\times}3\;cm^2$, respectively. For smaller field sizes, the cylindrical and plane parallel ionization chambers measure a smaller $S_{c,p}$ factor, as a result of the steep dose gradients across their sensitive volumes. The PDD values obtained with diamond detector and cylindrical ionization chamber for 6 and 10MeV photon beams agreed well ($\pm1.5%$) for field sizes greater than $4{\times}4\;cm^2$. For smaller field sizes, diamond detector produced a depth-dose curve which had a significantly shallower falloff than that obtained from the measurements of relative depth-dose with a cylindrical ionization chamber. For the measurements of beam profiles, a distortion in terms of broadened penumbra was observed with a cylindrical ionization chamber since diamond detector exhibited higher spatial resolution. The diamond detector with small sensitive volume, near water equivalent, and high spatial resolution is suitable detector compared to ionization chambers for the measurements of small field photon beams.

• Progress in Medical Physics
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• v.11 no.1
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• pp.1-18
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• 2000

For wedged photon beams, the variation of the wedge factor with field size was reported by several authors. However, until now such variation with field size had not been explained quantitatively. Therefore, the variation of the wedge factor was investigated by measuring outputs with field sizes increasing from 4 cm $\times$ 4 cm to 25 cm $\times$ 25 cm for open and wedged 6 and 10MV X-ray beams. The relative outputs for wedged fields to 10 cm $\times$ 10 cm have been obtained. The results show the Increase of the wedge factor caused by the change in fluence of high energy Photon beam with field size, up to 8.0% for KD77-6MV X-ray beam. This increase could be explained as a linear function of the irradiated wedge volume except small field size up to about 10 cm. In the cases of the narrow rectangular beam parallel to the wedge direction, the wedge factor decreases slightly with increasing field size up to about 10-15 cm due to a relatively reduced photon fluence from the change of the wedge thickness. We could explain the causes of a wedge factor variation with field size as the fluences of primary photon passed throughout the wedge, contributing to the dose at the central beam axis and that the fluences were affected by the gradient of the wedge with the change of field size. For clinical use, the formula developed to describe the wedge factor variation with field size has been corrected.

• Proceedings of the Korean Society of Medical Physics Conference
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• 2004.11a
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• pp.33-35
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• 2004

방사선치료를 위한 고에너지 광자선의 품질관리를 위해 사용하는 TLD의 광자선 선질에 대한 에너지 의존도를 몬테카를로 모사법을 사용하여 평가하였다. IAEA 선량보증사업에 이용되는 LiF TLD 및 홀더를 EGS4기반의 사용자 코드인 DOSIMETER 와 MCNP4C 몬테카를로 코드를 사용하여 기하학구조를 구성하고, Co, 4, 6,10 밑 15 MV 광자선을 시뮬레이션하였다. DOSIMETER계산 결과를 통해 TLD의 에너지 보정인자가 실험 데이터와 일치함을 확인할 수 있었으며, 이와 별도로 캡슐에 의한 교란량도 무시할 수 없음을 발견하였다.

• Journal of the Korean Magnetics Society
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• v.27 no.1
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• pp.18-22
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• 2017

The purpose of this study was to present an improved method of dose modulation over the increase of build-up for existing 6 MV photon beam. Two neodymium permanent magnets with a strength of 0.5 T (Tesla) were applied with a magnetic field perpendicular to the photon beam. The effects of dose on build-up region with or without the magnetic field were measured according to the magnet-to-magnet distance (MMS) and the magnet-to-surface distance (MSD). For MMS = 6 cm and MSD = 2.5 cm, $D_{0mm}$, $D_{2mm}$, $D_{5mm}$, and $D_{10mm}$ showed improved doses of 6.8 %, 14.6 %, 6.9 %, and 2.1 %, respectively, as compared with 6 MV open beam. In this study, the device with low strength magnetic field can be applied directly to the outside of the human body when the target volume located close to the skin is delivered with radiation. It is expected that the method of build-up modulation using a low strength magnetic field will be feasible in the clinical applications.

• Progress in Medical Physics
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• v.13 no.2
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• pp.69-73
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• 2002

Exposure measurement data with parallel plate ionization chambers were known to depend on the polarity ($k_{pol}$) effect. In this work, the polarity effect were investigated for three parallel plate ionization chambers with different volume. The ionization chamber was fabricated using acrylic plate for the chamber medium and printed circuit board for electrical configuration. The various sizes of the sensitive volumes designed so far were 0.9, 1.9, and 3.1 co. High voltage generator was fabricated using the conventional 9 V batteries to apply the high voltage (300-500 V) to the electrode of the parallel plate ionization chamber. The gap between two electrodes ranged from 3, 6, and 10mm. As the result of our experiment, the polarity effect was within 0.5% in photon beam and 1% to 3.5% in the electron beams. Among electron beams, 16 MeV beam, which had highest energy, showed less polarity effect than electron beams with other energies.

• Progress in Medical Physics
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• v.17 no.3
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• pp.179-186
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• 2006

Purpose: Photon beam data of linear accelerators in Korea are collected, analyzed, and a simple method for checking and verifying the dose calculations in a TPS are suggested. Materials and Methods: Photon beam data such as output calibration condition, output factor, wedge factor, percent depth dose, beam profile, and beam quality were collected from 26 institutions in Korea. In order to verify the accuracy of dose calculation, ten sample planning tests were peformed. These Include square, elongated, and blocked fields, wedge fields, off-axis dose calculation, SSD variation. The planned data were compared to that of manual calculations. Results: The average and standard deviation of photon beam quality for 6, 10, and 15 MV were $0.576{\pm}0.005,\;0.632{\pm}0.004,\;and\;0.647{\pm}0.006$, respectively. The output factors of 6 MV photon beam measured at depth of dose maximum for $5{\times}5cm,\;15{\times}15cm,\;20{\times}20cm\;were\;0.944{\pm}0.006,\;1.031{\pm}0.006,\;and\;1.055{\pm}0.007$. For 10 MV photon beam, the values were $0.935{\pm}0.006,\;1.031{\pm}0.007,\;1.054{\pm}0.0005$. The collected data were not enough to calculate average, the output factors for 15MV photon beam with field size of $5{\times}5cm,\;15{\times}15cm,\;20{\times}20cm\;were\;0.941{\pm}0.008,\;1.032{\pm}0.004,\;1.049{\pm}0.014$. There was seven institutions $e{\times}ceeding$ tolerance when monitor unit values calculated from treatment planning system and manually were compared. The measured average MU values for the machines calibrated at SAD setup were 3 MU and 5 MU higher than the machines calibrated at SSD for 6 MV and 10 MV, respectively except the wedge case. When the wedges were inserted, the MU values to deliver 100 cGy to 5 cm depends on manufactures. When the same wedge angle was used, Siemens machine requires more MUs then Varian machine. Conclusion: In this study, photon beam data are collected and analyzed to provide a baseline value for chocking beam data and the accuracy of dose calculation for a treatment planning system.

• Journal of the Korean Society of Radiology
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• v.17 no.4
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• pp.507-514
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• 2023

The purpose of this study is to find a formula that can easily calculate the effective photon energy in the X-ray beam of mammography. The tube voltage measured for each set tube voltage was obtained using the X2 MAM Sensor. The mass attenuation coefficient for aluminum of the aluminum filter was obtained from the half value layer measurement from each measured tube voltage X-ray beam. The mass attenuation coefficient of aluminum obtained from each measured tube voltage X-ray beam was corresponded to the mass attenuation coefficient of aluminum for each photon energy obtained from NIST. The photon energy corresponding to the matching mass attenuation coefficient was determined as the effective photon energy. The formula for calculating the determined effective photon energy was obtained by polynomial matching of the effective photon energy for each tube voltage in the Origin pro 2019b statistical program as y = 28.98968-1.91738x + 0.07786x2-0.000946717x3. Here, x is the measuring tube voltage and y is the effective photon energy. The calculation formula of the effective photon energy of the mammography X-ray beam obtained in this study is considered to be very useful in obtaining the interaction coefficient between the X-ray beam and a certain substance in clinical practice.

• The Journal of Korean Society for Radiation Therapy
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• v.17 no.2
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• pp.161-166
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• 2005

Purpose : Electron is used for the treatment of skin cancer, breast cancer, and head and neck cancer in clinic. Our study is performed to check the isodose distribution in source surface distance(SSD)and source bolus distance(SBD)setup, nipple influence to isodose distribution of electron, junctional area isodose variation of photon and electron field. Materials and Methods : The electron dose distribution measures the diameter for 20 cm hemisphere paraffin phantom 2 made. It inserted the film between 2 paraffin phantom and it investigated it got radiation and dose distribution curve. Results : The 8% of isodose difference is with the surface distance(SSD)and source bolus distance(SBD)setup. The electon when the nipple exists inside the field, as nipple size it cuts the bolus and when it puts out and there is a possibility of getting the dose distribution which is homogeneous. When in the junction of electron and photon it uses the bolus it uses in the electron field whole, there is a possibility of getting the dose distribution which is homogeneous. Conclusion : The dose distribution decrease from the SBD setup. To reduce the influence of nipple, corresponding volume of bolus should be removed. And bolus covering all the electron field reduced hot and cold spot of junctional area of photon. In the future becomes the research which sees an effective electron therapy.

• Progress in Medical Physics
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• v.17 no.1
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• pp.54-60
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• 2006

In order to apply the TRS-398 dosimetry protocol developed by IAEA we directly calculated the quality correction factors for high energy photons. The calculations were peformed for seven commercial cylindrical chambers (A12, IC70, N23333, N30001, N30006, NE2571, PR06C/G). In comparison with quality correction factors given by TRS-398 our results were in good agreement within ${\pm}0.3%$ (maximum ${\pm}0.3%$) for all chambers and photon qualities.